What is your confidence to internally built Watch Dog?
I prefer it to an external.

[A]And I use internal Watch Dog.
And microcontroller is hanging up :(
1)In some versions the ISP code does not pet the puppy. Thus you need to enable the dog AFTER the decision program/run is taken.
2) the time for the 668 dog (I guess the 669 is the same) is shorter than the 1232. Did you take that into account?
3) if you are using the Intel Kluge dog (PCA4) all bets are off, use the REAL dog.

I made all prevention steps as it was frequently discussed on these form (capacitor over supply pins, short connections wires etc...).
excellent

[B]Finally I give it up all hope and I connect Strobe Input to output pin of microcontroller. Strobe Input of DS1232 is now trigged via software.
At last circuit works perfectly now.
It is next to impossible to make a supervisor with WD run together with an internal dog That you have to stroke the external dog is self evident. When using a chip with internal memory only (I guess that is what you are doing) you usually do not get ALE.

Obviously internal Watch Dog is not efficient.
My explanation is:
Watch Dog which must be started across software is not a good solution.
In critical situation maybe software has no time to start Watch Dog.
Possible it hangs immediately after reset, before Watch Dog activation.
All the above: start the dog as one of the first things after the jump from 0 (Keil C: modify startup.a51.

[A] and [B] above indicate to me that the problem was not the internal dog, but the dog in the 1232 not getting petted.

Erik